Many vehicles today have electric power steering systems. Electric power steering (EPS) systems typically use an electric motor to provide a steering assist to a driver of the vehicle, thereby reducing effort by the driver in steering the vehicle.
Smooth Road Shake (SRS) is one type of objectionable vibratory response possible within an EPS leading to customer complaints. SRS is caused by internal periodic excitation such as tire/wheel imbalance, tire irregularities, brake rotor imbalance and lack of precision piloting of the rotating members. SRS typically occurs over a band of frequencies extending from 8 to 22 Hz, which depend on vehicle speed but occur typically in a range from about 72-145 kilometers-per-hour (kph) (approximately 45-90 miles-per-hour (mph)).
The presence of the mechanical torsional vibrations originating in the periodic excitation by the corners, i.e., the steerable or non-steerable wheel assemblies and related suspension and brake components at the corners of the vehicle, at lower orders of tire rotation, i.e., SRS, without any intervention by the EPS motor can result in a degradation in the perception of the steering response. Although not influencing the operation of the vehicle, these perceptible nuances can be large enough to convey a degree of dissatisfaction with the feel of the steering system as the steering wheel is rotated during mild steering maneuvers.
In certain vehicles equipped with EPS it is possible to actively attenuate via feedback control arrangements relatively narrowband torsional vibrations that are typical of SRS. This is generally accomplished using either proportional or integral feedback control arrangements or combinations thereof. Feedback control may have slow response following transient vehicle maneuvers: starting from a stopped condition, reversing, rapidly changing vehicle speed, etc. The response of a feedback control scheme can be improved by increasing control gain, but large gain introduces instability. Feed forward control offers faster response with a higher degree of fidelity and without the stability issues of feedback control. Nonetheless, these control arrangements have not seen implementation because of the unavailability of necessary data.
Accordingly, it is desirable to provide EPS systems and methods providing enhanced steering perception in vehicles, for example that provide an improved feel for the steering system during vibratory conditions such as occur with SRS attenuation in an EPS, through feed forward control arrangements. It is also desirable to provide program products and systems for improved steering perception in vehicles, for example that provide an improved feel for the steering system during vibratory conditions such as occur with SRS attenuation in an EPS, through feed forward control arrangements. Furthermore, other desirable features and characteristics of the present disclosure will be apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.